Switching regulator

Abstract

A switching regulator is disclosed which is designed so that a negative feedback is applied to the base of a transistor constituting an oscillator adapted for chopping a DC voltage, only during a period of time which is required to effect pulse width control when the transistor is switched from conduction to non-conduction. A control circuit may also be provided which is arranged to compare the output of a current detecting circuit for detecting a current proportional to a current for driving a transformer with the output of an error voltage amplifier for amplifying an output resulting from comparison of a rectified version of the AC output of the transformer with a reference voltage. The foregoing control circuit is also arranged so that when the output of the current detecting circuit exceeds the output of the error amplifier, a trigger signal is imparted to cause the oscillator to be changed from the on state to the off state.

What is claimed is: 
     
       1. A switching regulator comprising a blocking oscillator circuit for converting into an intermittent form a DC voltage supplied from an input power source to thereby drive a transformer; a rectifier circuit for rectifying an AC voltage output derived from said transformer; a voltage comparator circuit for comparing the DC output voltage derived from said rectifier circuit with a reference voltage to provide an output corresponding to the deviation of said DC output voltage from said reference voltage; an error voltage amplifier circuit for amplifying the output of said voltage comparator; a current detecting circuit for detecting a transformer driving current of said blocking oscillator circuit; and a control circuit means for comparing the output of said current detecting circuit with the output of said error voltage amplifier circuit and applying to said oscillator circuit a trigger signal for causing said oscillator circuit to be changed from the on state to the off state only when the output of said current detecting circuit exceeds the output of said error voltage amplifier circuit. 
     
     
       2. A switching regulator according to claim 1, wherein said current detecting circuit is connected in series with the primary winding of said transformer. 
     
     
       3. A switching regulator according to claim 1, wherein said current detecting circuit is arranged to detect a current proportional to a current flowing through a choke transformer provided in a smoothing circuit including a free-wheeling diode. 
     
     
       4. A switching regulator according to claim 1, wherein the operational range of said error voltage amplifier circuit is limited by a voltage proportional to the DC output voltage derived from said rectifier circuit.